Hyponatremia

Serum Na <130

Classification:
Hypovolemic
- More sodium lost than water, i.e. cystic fibrosis, third spacing, diuretic abuse, adrenal insufficiency

Euvolemic
– SIADH, hypothyroidism, water intoxication, glucocorticoid deficiency

SIADH Criteria: Think scarce pee
1) low serum Na (<135)
2) high urine sodium (>20 meq/l)
3) urine osm (275)

Correction:
1) Fluid restrict (1200ml/m2/dayà800à400àinsensibles)
2) Consider 3% NaCL 3-4 ml/kg
3) Consider loop diuretic

Hypervolemia
- Edematous states, i.e. CHF, cirrhosis, nephritic syndrome, and renal failure

Pseudohyponatremia
- Increased serum lipids or proteins, or in diabetic for every increase in glucose >100 mg/dl of 100 mg/dl Na is lowered by 1.6 mEq/L

Diagnosis:
- Urinary sodium will help you distinguish amongst the various etiologies

Management:
- Avoid rapid correction since it may lead to central pontine myelinolysis
- Treat immediately symptomatic hypovolemia i.e- poor peripheral pulses, delayed capillary refill, orthostatic changes with 20 ml/kg NS
- If NEUROLOGIC SX i.e. Seizures, severe confusion, coma, or signs of brainstem herniation and Na <125 give hypertonic Saline 3%, 3 ml/kg IV infusion over 10 mn
- In general, increase of 4-6 mEq/L in serum sodium level is sufficient to arrest progression of symptoms in severe hyponatremia.

Required volume = (Desired Change in Serum Sodium)(TBW) / (Na in IV Fluid – Current Serum Na), where TBW = Body Weight X 0.6

For example, a 60-kg woman with serum sodium level of 113 mEq/L would require 360 mL of hypertonic saline

In general, 300-500 mL of 3% NaCl is reasonable dose in most adult patients with severe symptomatic hyponatremia

Give IV over first 1-2 h until resolution of seizures or herniation

If asymptomatic may correct much slower 10 mEq/L/hr
o If hypovolemia, replace Na with NS or D5 NS
o If euvolemia- limit water intake to 2/3 maintenance and treat underlying condition if SIADH
If hypervolemic restrict fluids to 2/3 maintenance; give Lasix 1mg/kg IV if pulmonary